Method of making electrical contacts for and passivating a semiconductor device

ABSTRACT

THE METHOD OF MAKING ELECTRICAL CONTACTS FOR AND PASSIVATING A SEMICONDUCTOR DEVICE INCLUDES THE STEPS OF DEPOSITING THEREOVER A LAYER OF POLYCRYSSTALLINE SILICON MATERIAL AND SELECTIVELY DOPING THE POLYCRYSTALLINE SILICON MATERIAL AT LOCATIONS WHEREAT THE ELECTRICAL CONNECTIONS ARE TO BE MADE TO RENDER IT CONDUCTIVE THEREAT. IN THE CASE OF SEMICONDUCTOR DEVICES HAVING A PASSIVATING LAYER OF SIO2 OR THE LIKE THEREOVER, THE SIO2 MUST FIRST BE REMOVED IN THOSE AREAS WHEREAT THE ELECTRICAL CONTACTS ARE TO BE FORMED.

"UnitedStates Patent Omce 3,806,361 Patented Apr. 23, 1974 U.S. Cl.117-212 7 Claims ABSTRACT OF THE DISCLOSURE The method of makingelectrical contacts for and passivating a semiconductor device includesthe steps of depositing thereover a layer of polycrystalline siliconmaterial and selectively doping the polycrystalline silicon material atlocations whereat the electrical connections are to be made to render itconductive thereat. In the case of semiconductor devices having apassivating layer of SiO2 or the like thereover, the SiO'z must rst beremoved in those areas whereat the electrical contacts are to be formed.

BACKGROUND OF THE INVENTION This invention relates generally to methodsfor making electrical contacts for semiconductor devices and moreparticularly to such methods for `making electrical connections tosemiconductor devices which have been passivated.

Presently, when making electrical contacts for a semiconductor devicehaving an SiO2 or the like passivation layer deposited thereover, asection of the SiOZ layer is first removed. Thereafter, the area fromwhich the SiOz material was removed is lled With a conductive materialsuch as, for example, aluminum, to which an electrical connection can bemade.

While the above described technique provides an adequate electricalcontact for the semiconductor device, the area whereat the aluminum isdeposited, is not passivated and is susceptible to contamination byforeign particles. Contamination of the area can cause malfunction ofthe semiconductor device at a later time.

SUMMARY OF THE INVENTION Accordingly, it is a general object of thepresent invention to provide a new and improved method for makingelectrical contacts for semiconductor devices, which overcomes thedrawbacks of the prior art.

It is another object of the present invention to provide a new andimproved method for forming electrical contacts for semiconductordevices wherein the sites of the electrical contacts are passivated.

Briefly, the method according to the invention comprises the steps ofremoving from a passivated semiconductor device, an area of passivatingmaterial to expose the semiconductor material therebeneath whereat anelectrical contact is to be formed, Thereafter, a layer ofpolycrystalline silicone is deposited over the semiconductor deviceincluding the exposed area. Subsequent to the deposition of thelast-mentioned material, aluminum or the like metal is sintered in todope the polycrystalline silicon covering the exposed area, therebyproviding a conductive area through the polycrystalline silicon whereatan electrical connection may be made to the semiconductor materialtherebeneath. The polycrystalline silicone serves both as a conductorfor making the electrical contact and as a passivating material for thedevice.

It is not necessary that a passivation layer of material be appliedprior to the application of the polycrystalline silicon, however, it isadvantageous since the gain of the semiconductor device may be alectedvw'thout the highly resistive passivating layer such as, SiO2, beingprovided beneath the polycrystalline silicone.

DESCRIPTION OF THE DRAWING In the drawing:

FIGS. 1-7 are cross-sectional, fragmentary views of a semiconductordevice as it appears during the various stages of the method accordingto the invention for preparing electrical contacts therefor and forpassivating the contact areas.

DETAILED DESCRIPTION Referring now to the drawing in greater detail,FIGS. 1-7 illustrate a semiconductor device, designated generally `bythe numeral 10, herein shown as a transistor component having a lowersubstrate or wafer 12 of silicon or the like material. Deposited overthe wafer 12, are layers 14, 16 of P and N type semiconductor material,respectively. A P type area 18 is diffused into the upper N type layer.In the case of the device shown, area 18 forms the emitter portion ofthe transistor while areas 16 and 14 form the base and collectorsthereof, respectively. The use of a transistor component in the drawingof the instant application is for illustrative purposes only since themethod according to the invention may be applied to semiconductordevices other than transistors.

During the formation of the devices, a passivation layer 22 of SiO2 orthe like material may be deposited over the surface of the device. Thehighly resistive passivation material maintains the device contaminantfree. In the production of semiconductor devices of the type shown,i.e., mesa type semiconductor devices, the semiconductor material of thevarious layers is etched away to form valleys, such as 20, whichseparate the remaining semiconductor devices. The etching also removesthe passivation material from the junction in the valley.

To provide electrical contacts for the various layers of thesemiconductor device, areas of the SiOz beneath which such contacts areto be provided, are removed to expose the semiconductor layers (see FIG.3). Conventionally, metal is deposited in the openings, such as 24,formed in the Si02 to make physical contact with the semiconductormaterial. In the latter technique, however, the valleys and contactareas remain unpassivated and therefore are susceptible to contaminationwhich could aiect the operation of the semiconductor device.

In the method according to the invention, subsequent to the removal ofthe SiOZ passivating material to form openings 24 (FIG. 3), a layer 26of polycrystalline semiconductor material, preferably polycrystallinesilicon, is deposited over the Si02 layer (FIG. 4). The last-mentionedlayer can be deposited over the semiconductor device by passing thedevice through a heated chamber having an atmosphere of SiCl4 and H2.The polycrystalline silicon layer formed over the semiconductor devicefurther passivates the device including the areas 24 and 20 exposed bythe removal of the semiconductor material and SiOz prior thereto.

Subsequent to the deposition of the polycrystalline silicon, a layer 28of aluminum or the like conductive metal is provided thereover (FIG. 5).The metallized layer can be sputtered or vacuum deposited onto thesemiconductor device in a `well known manner, or any other suitabletechnique may be used if desired. Thereafter, the conductive layerprovided over the areas adjacent those areas to be used as electricalcontact areas, is etched away, leaving only the metallized areas, suchas 30 on the polycrystalline silicon, which are in alignment with theopenings 24 in the SiO2 therebeneath. The removal of the unwantedmetallized areas may be accomplished by overlaying the aluminum afterdeposition thereover, with a layer of impervious material'such as wax,or the like. Thereafter, the

wai is removed Vat those areas vvhichareA not to be"usedVpolycrystalline silicon areas, such as 32, beneaththe sites ofconductive metal, rendering those areas conductive, thereby making anelectricall connection possible to the semiconductor materialtherebeneath.

The doped polycrystalline silicon serves both as a conductive contactarea whereat electrical connections to the semiconductor device may bemade as well as passivating material to maintain the area contaminantfree.

While the above description was given in conjunction with asemiconductor device having a passivation layer of SiOz thereover, it isnot necessary to provide sucha layer in addition to the polycrystallinesilicon layer. Instead, the polycrystalline silicon layer may bedeposited over the semiconductor device 10 as shown in FIG. l.Thereafter, the steps illustrated in FIGS. 5-7 may be taken to provideelectrical contacts for the device'.

I claim: 1. The method of making electrical contacts for semiconductordevices comprising the steps of:

depositing a layer of polycrcystalline silicon material over saidsemiconductor device; depositinng an aluminum layer at locations whereatelectrical contacts are to be formed; and heating said semiconductordevice to causesaid aluminum to be sintered into said polycrystallinematerial thereat thereby rendering said area conductive and makingelectrical connections with said semiconduc-` tor material. i 2. Themethod of claim 1 wherein said semiconductor device includes apassivation layer providedthereover `and further including the step ofremoving said passivation' material at said desired locations prior tothe deposition of said polycrystalline material over saidsemiconductoriy device.

3. The method of makingelectrical contacts for a semi-1u conductordevice having a highly resistiveupassivating material depositedthereover, comprising the steps '0f: removing said passivating materialat predetermined locaing material has been removed, and ydoping saidpolycrys-I talline material at locations alignedwith said predeterminedlocations to render the polycrystalline vmaterial thereat electricallyconductive, thereby to make electrical Vcontact with said semiconductormaterial"thereb'eneath.l

4. The method of claim 3 wherein the doping of said polycrystallinematerial comprises the steps of depositing metallic material over saidpolycrystalline layer at loca- 'tions aligned with said predeterminedllocations and heat-A comprises the steps of: depositing said lmetallicmaterialy over said polycrystalline layer, applying an impervious layerof material over predetermined areas of said metallic material, etchingaway. thegmetallic material -not covered by said impervious layer,removing said impervious layer over the remaining metallic materialsubsequent to etching, and heating said semiconductor device forsintering said metal into said polycrystalline material at saidpredetermined locations.

6. The method of claim 5 wherein said semiconductor"I device is heatedat a temperature in the range of 40G-500 C. for sintering the conductivemetal into said polycrystalline material.

` prising the steps of 7. The method of making electrical contact forand passivating a semiconductor device which includes thereover a layerof highly resistive passivating material comremoving said highlyresistive passivating material at predetermined locations; depositing alayer of polycrystalline silicon material overv the surface of saidsemiconductor device and said remaining passivating material; forming alayer of aluminum over said predetermined locations; and heating saidsemiconductor device to sinter the aluminum into said polycrystallinematerial to render the polycrystalline material conductive thereat,thereby to complete an electrical connection `with said semiconductordevice.

References Cited UNITED'STATES PATENTS Y 3,189,973 t 6/1965 Edwards117-201 3,481,776 :l2/1969 Manchester ll7212 3,653,120 4/1972 ySireine v317-234 L 3,667,008 ,V5/1972 Kartack 317-235 AT 3,703,420 11/1972 Vora117-212 LEN D. 'RosDoL, Primary Examiner ESPOSITO, Assistant `ExaminerUs. C1. XR. i

